No. 463.] STUDIES ON PLANT CELL. VI. 453 



upon information which in point of completeness falls very far 

 short of our knowledge of the groups above. Indeed, no forms 

 have been studied with the detail that is known in higher groups 

 chiefly for the reason that the investigator is forced to deal with 

 very small nuclei and mitotic figures whose chromosomes are 

 exceedingly minute and because of various technical difficulties. 

 The theories in general fall into two groups : (i) those which 

 have an obvious basis in attempts to reconcile events with the 

 processes of gametogenesis in animals, and (2) those proceeding 

 from the view that for phylogenetic reasons the periods and phe- 

 nomena of gametogenesis in the lower plants should correspond 

 with those of the higher. 



We may pass over with a few words the early crude attempts 

 to establish structures for plants comparable to the polar bodies 

 of animals. For example at the conclusion of oogenesis in some 

 algae (e. g., Vaucheria, CEdogonium) a globule of slime is exuded 

 with the opening of the oogonium. It was suggested that such 

 material is thrown off from the egg but we now know that it is 

 not protoplasmic in character but is apparently derived from a 

 softening of the cell wall. Then the ventral canal cell has been 

 compared to a polar body but it seems clear now that all of 

 the canal cells are homologous and a part of what was form- 

 erly an extensive gametogenous tissue within the archegonium. 

 Then the small group of cells cut off below the oogonium of the 

 Charales and the fragmented nuclear material in the trichogyne 

 of the red algae have been compared to substance thrown off 

 from the egg but without any knowledge of the nuclear struc- 

 ture. Finally the nuclear degeneration which is a very conspic- 

 uous feature of oogenesis in certain groups whose oogonia are 

 multinucleate (Peronosporales, Saprolegniales, Pelvetia, etc.) 

 has been considered related to reduction phenomena. But the 

 nuclei in all of these forms bear every evidence of being in each 

 type homologous structures whose large numbers have a phylo- 

 genetic raison d'etre and the extensive degeneration is associated 

 with the principles of sexual evolution which tend to conserve 

 protoplasm for the good of a lesser number of gamete nuclei 

 even to the sacrifice of others that are potentially equivalent. 



We will now consider the few instances among the thallo- 



